POS0341 CONSENSUS-DRIVEN DEFINITION FOR UNEQUIVOCAL SACROILIITIS ON RADIOGRAPHS IN JUVENILE SPONDYLOARTHRITIS
Authors: P. F. Weiss, T. G. Brandon, R. G. Lambert, D. M. Biko, N. A. Chauvin, M. L. Francavilla, N. Herregods, A. M. Hendry, W. P. Maksymowych
Journal: Annals of the Rheumatic Diseases (2022)

Background Radiographs are not a sensitive or reliable imaging tool for detection of early sacroiliitis in juvenile spondyloarthritis (JSpA). However, radiographs are still commonly performed in some areas due to difficulty in accessing MRI. As such, radiographs were included in the imaging data considered for an axial disease classification criteria development study, but only when there was no suitable MRI available. Objectives We aimed to define criteria for unequivocal evidence of sacroiliitis on pelvic radiography in skeletally immature children and adolescents for use in classification criteria. Methods Subjects were a cohort of JSpA patients with suspected axial disease. All subjects had symptom onset prior to age 18 years and underwent MRI as part of a diagnostic evaluation for axial disease; a subset of subjects also had a dedicated pelvic radiograph. Using a web-based interface, 6 musculoskeletal imaging experts, blinded to clinical details, reviewed the radiographs and graded them according to the modified New York (mNY) criteria. A two-way random effects intraclass correlation coefficient (ICC) was used to assess agreement. Next, the central imaging team underwent an iterative consensus process to define unequivocal evidence of sacroiliitis on pelvic radiography in skeletally immature children. Radiographs with at least two raters assigning a non-zero mNY grade were re-reviewed for the presence/absence of “unequivocal evidence of sacroiliitis” according to the consensus definition. Agreement was assessed with Fleiss’s kappa statistic with agreement interpreted as poor ≤0.40, fair 0.41-0.59, good 0.60-0.74, and ≥0.75 excellent. Sensitivity, specificity, and positive and negative predictive values (PPV, NPV) were calculated to assess performance of the novel definition using structural lesion typical of juvenile axial disease on MRI as the reference standard (erosion in ≥3 sacroiliac joint (SIJ) quadrants or at least one of the following lesions in ≥2 SIJ quadrants: sclerosis, fat lesion, backfill, ankylosis). Results Radiographs from 120 subjects, 61% male, median age 14.7 years (range 6.7-20.1 years), had an AP dedicated pelvic radiograph available for scoring. The ICC for mNY grade amongst 6 central raters was fair for joints with at least one rater reporting a non-zero grade (0.45, 95% CI: 0.34-0.57). After multiple iterations and discussion, the consensus definition of unequivocal sacroiliitis by radiograph in skeletally immature children and adolescents was deemed “Unequivocal lesion (erosion, sclerosis, or ankylosis [partial or complete]) that must include at least one iliac bone. When sclerosis is present in isolation, if measurable, should extend ≥5mm from the joint surface. The decision may be influenced by the presence of other lesions, which in themselves do not suffice to meet the criterion.” Sixteen radiographs were assessed using the consensus definition. 8 (50%) were rated as unequivocal sacroiliitis and Fleiss’ kappa statistic was good at 0.61 (95% CI: 0.41-0.80). Across raters, the sensitivity, specificity, PPV and NPV of the consensus definition on radiograph using structural lesions typical of sacroiliitis on MRI as the reference standard were 80% (95%CI: 44.4-97.5), 100% (95% CI: 54.1-100), 100% (63.1-100) and 75% (95% CI:34.9-96.8), respectively. Conclusion We propose a consensus-derived definition of unequivocal sacroiliitis by radiography in skeletally immature children and adolescents with good expert rater agreement. Additionally, the consensus-definition had moderate to high sensitivity and PPV and high specificity and NPV with typical structural lesions on MRI as the reference standard. This definition has applicability to JSpA axial disease classification criteria when MRI is unavailable. Figure 1. Examples of radiographs with unequivocal evidence of sacroiliitis in skeletally immature children as indicated by definite erosions of both iliac bones (A and B) and definite iliac sclerosis (A). Disclosure of Interests Pamela F. Weiss Consultant of: Pfizer Novartis Biogen Lilly (All &lt; $5K in the past fiscal year), Timothy G. Brandon: None declared, Robert G Lambert Paid instructor for: Novartis, Consultant of: CARE Arthritis, Calyx, Image Analysis Group, Novartis, David M. Biko Employee of: Merck (1998 to 2000), Nancy A. Chauvin Employee of: Forest Pharmaceuticals - Research scientist (1996) and Novartis - Pharmaceutical sales representative (1997), Michael L. Francavilla: None declared, Nele Herregods: None declared, Alison M. Hendry: None declared, Walter P Maksymowych Speakers bureau: Abbvie, Eli-Lilly, Janssen, Novartis, Pfizer, UCB Pharma, Consultant of: AbbVie, Boehringer Ingelheim, Celgene, Eli Lilly, Galapagos, Janssen, Novartis, Pfizer, UCB Pharma, Grant/research support from: Abbvie, Novartis, Pfizer